A conventional multi-room type air-conditioning system, that comprises one outdoor unit and a plurality of indoor units coupling to the outdoor unit, employs a variable capacity compressor, and controls the variable capacity of the compressor disposed in the outdoor unit responsive to loads requested from the indoor unit.
The above conventional air-conditioning system is detailed hereinafter by referring to the attached drawings.
FIG. 7 depicts a refrigerating cycle of the conventional multi-room type air-conditioning system.
In FIG. 7, a variable frequency compressor 103 driven by an inverter (hereinafter called "compressor"), an outdoor heat exchanger 104, and a four-way valve 105 for selecting functions, i.e., cooling/heating modes, are provided in an outdoor unit 101. Indoor heat exchangers 106a, 106b and 106c are provided in indoor units 102a, 102b and 102c respectively. The outdoor unit 101 is coupled to the indoor units 102a, 102b and 102c with liquid branch pipes 108a, 108b, and 108c as well as gas branch pipes 110a, 110b and 110c, where a liquid main pipe 107 and a gas main pipe 109 are both disposed within the outdoor unit 101, and both the main pipes branch into the above branch pipes. In the liquid branch pipes 108a, 108b and 108c, flow-control valves 111a, 111b and 111c are provided so that valve opening positions can be controlled by pulses using stepping motors. The indoor units 102a, 102b and 102c comprise indoor temperature sensors 117a, 117b and 117c that detect their room temperatures, and operation setting circuits 118a, 118b and 118c with which a user can set an operation mode (cooling or heating), a desirable temperature, start and stop.
A method of controlling a frequency of the compressor in this refrigerating cycle is described hereinafter.
FIG. 8 is a block diagram depicting the controlling process, and FIG. 9 depicts a divisional temperature zone of .DELTA.T, which is a difference between the room temperature Tr and a set temperature Ts.
In the indoor unit 102a, first, an output of the indoor temperature sensor 117a is fed into a room temperature detection circuit 121, then tapped off therefrom as a temperature signal and fed into a differential temperature calculating circuit 122. On the other hand, the set temperature and the operation mode instructed by the operation setting circuit 118a are determined by a setting determination circuit 123, and fed into the differential temperature calculation circuit 122, where a temperature difference .DELTA.T (=Tr-Ts) is calculated and converted into a load number, i.e., value Ln, as shown in FIG. 9, which is taken as a differential temperature signal. For example, in the cooling operation, Tr=27.3.degree. C., Ts=26.degree. C., .DELTA.T=1.3.degree. C. and which makes Ln=6. An ON-OFF recognition circuit 124 recognizes a start (ON) or a stop (OFF) of the indoor unit 102a, where the start and stop are set by the operation setting circuit 118a. Further, a rated capacity of the indoor unit 102a is stored in a rated capacity storing circuit 125. These signals including the rated capacity signal, differential temperature signal, operation mode signal and ON-OFF recognition signal, are fed from a signal transmitting circuit 126 into a signal receiving circuit 127 of the outdoor unit 101. The same signals are fed from the indoor units 102b and 102c into the signal receiving circuit 127. The signals received in the circuit 127 is fed into a compressor frequency calculation circuit 128.
In the compressor frequency calculation circuit 128, load constants of each indoor unit are taken from a load constant table 130 shown in FIG. 10 using the rated capacity signal, differential temperature signal, operation mode signal and ON-OFF recognition of each indoor unit. A frequency of the compressor 103 is determined through multiplying the sum total of these load constants by a constant which is predetermined through experiments.
The frequency of compressor is thus controlled responsive to the sum total of requested capacity from each room.
This conventional system, however, has the following problems.
The capacity of the compressor is controlled through an easy calculation, such as a linear equation, responsive to load requests from each room, therefore, the capacity of the compressor is not optimally controlled both in an every-room-operation and a single-room-operation, i.e., when the every-room-operation is controlled by a high frequency, the frequency is too high for the single-room-operation. On the other hand, when the frequency is set optimally for the single-room-operation, the every-room-operation is driven by a rather lower frequency and results in a short capacity operation.
The present invention addresses the above problem and aims to realize operations with the best efficiency both in the every-room-operation and the other operations with an optimal frequency of the compressor.